Numerous patents have issued on powered wheel chairs, each disclosing one or more features intended to solve a problem or problems commonly encountered by a wheel chair occupant. By way of example, and without attempting to be exhaustive, reference may be made to the following:
French Pat. No. 2,399,822 discloses a motorized wheel chair having powered main wheels at its opposite sides rotating on a common axis under the seat, at least one castered wheel located forward of the seat, and a pair of castered wheels some distance behind the seat. The front castered wheel is upwardly retractable to enable the wheel chair to move up onto a curb under its own power, and the seat can be raised and lowered to suit the occupant's convenience. However, the location of the front wheel and of the footrest are such that one or both of them are in the way of the occupant's feet during transfer between the wheel chair and another seat. The wheel chair structure as a whole is undesirably long from front to rear and an inherently large turning radius further makes it unsuitable for confined spaces such as toilet stalls and elevators.
U.S. Pat. No. 2,849,051 discloses a powered wheel chair wherein the seat member of the chair element can be raised, lowered, and tilted to some extent, the back rest can be tilted independently of the seat member to be brought to a reclining position, and the footrest is adjustable as to height and position but nevertheless cannot be brought to a position in which it is out of the way of the occupant's feet during transfer between the wheel chair and another seat.
U.S. Pat. No. 4,119,163 discloses a self-propelled wheel chair capable of climbing a curb and having a chair element that can be raised and lowered; but, as in the case of the above mentioned French patent, a front wheel and the footrest are in the occupant's way during transfer between the wheel chair and another seat.
U.S. Pat. No. 3,807,795 discloses a motorized wheel chair that has the seat member and back rest of its chair element so connected and so actuatable that the occupant can be brought to a standing position. The device is intended for those who are infirm rather than for those who cannot control their legs, and, again, it does not facilitate transfers between the wheel chair and another seat.
The problem of transfer that is repeatedly mentioned above is addressed in U.S. Pat. No. 3,952,822, wherein the chair element is mounted to swivel on a chassis that has power driven wheels at its opposite sides and has a steerable front wheel asymmetrically located near one side of the chassis and a footrest alongside that steerable wheel, adjacent to the other side of the chassis. As the chair element is rotated about its swivel axis, the occupant's feet are carried away from the footrest and the steerable front wheel. However, the advantage of the device with respect to facilitating transfer is offset by marked disadvantages, one of which is apparent from the patent itself. Because of the asymmetrical location of the front wheel, the device lacks stability, and therefore auxiliary support wheels are mounted on the chassis, at its side opposite the steerable wheel, one behind the main wheel, the other in front of it. These support wheels are normally spaced above the surface on which the device rides, and they engage that surface only when the device tilts to a certain extent. They may prevent the chair from tipping over, but they do permit a certain amount of sideward tilting that can give the occupant feelings of insecurity. The disclosed structure provides for forward and rearward adjustment of the seat relative to its swiveling axis but does not provide for heightwise adjustment, although adjustability of the seat in height is of particular importance in facilitating transfer.
One need only think about the occasional need for a wheel chair occupant to transfer between a wheel chair and a toilet seat to understand the great importance that attaches to transferring safely, easily and without assistance between a wheel chair and another seat. For any such transfer three factors are essential to the wheel chair occupant: the wheel chair must be securely confined against any horizontal movement; there should be nothing in the way of the occupant's feet and legs to hamper or impede the transfer; and the seat member of the wheel chair must be adjustable as to height because the seat to which the occupant is transferring must be at the same height as the one from which transfer is being made or a little lower--never higher.
Most conventional wheel chairs have castering front wheels and retractable footrests that project in front of the main wheels. Usually the footrests are retracted by swinging them upward, and in that case they can present more of a problem during a transfer than if they are left in their operative positions. In any event, a wheel chair occupant's disability may. make manual retraction of footrests difficult or impossible.
During transfer, the occupant tends to impose high lateral forces on the wheel chair that must be resisted by secure braking. Normally, castered front wheels cannot be confined against rotation or swiveling, and they therefore allow highly leveraged horizontal forces to be applied to the main wheels that can overcome a braking force on them.
Adjustability of seat height must be sufficient to bring the wheel chair seat member down to the level of the lowest seat to which the occupant might transfer and up to a level at which the occupant has comfortable access to a counter or the like that is intended for use by standing persons.
Almost invariably a toilet is located in a confined space in a bathroom or stall, and therefore another essential of a satisfactory wheel chair is extreme maneuverability, including capability for turning around on the spot. In this respect it will also be obvious that the overall length and width dimensions of the wheel chair should be as small as possible.
What might be considered "roadability" of a motor driven wheel chair is also important. It must be capable of moving forward at a reasonably fast speed; it should provide for easy and accurate one-handed control of speed, forward and rearward direction and turning; and--perhaps most important--it should be extremely stable and resistant to tipping over.
Stability of the wheel chair when it is braked as well as when it is rolling is of the utmost importance when the wheel chair is used as the driver's seat of a specially equipped van or the like that the wheel chair occupant drives, since the wheel chair must then be capable of supporting substantially high forces in every horizontal direction.
Satisfying these requirements poses a number of problems with respect to the structure of the wheel chair itself. The conventional source of power for a motorized wheel chair--and the only one known to be practical for the purpose--comprises one or more rechargeable batteries. Storage batteries are of course notoriously heavy and bulky, and batteries capable of storing enough energy for a day's operations occupy a substantial volume. In addition to the batteries, the wheelchair chassis must support motors or other actuators for driving the wheels, for raising and lowering the chair element, and for such additional movements or operations as may be required. All of this equipment must be so arranged that it is as compact as possible, does not interfere with mechanism for raising and lowering the seat, and ensures a low center of gravity and good riding stability for the device. The occupant of the wheel chair should be able to control all movements and other operations of the chair, preferably by means of control instrumentalities that are grouped to be accessible to one hand and are self-explanatory in relation to the functions that they control.